Reasons

It is strange to use diesel locomotives in space (for obvious reasons) - with all of this hi-tech materials new trains are needed.
Vacuum/low pressure and low-gravity
Using magnetic power to stay on tracks in space and even in high-speed
Electric power is easier to get in space and it does not need oxygen

Detail

New locomotives has internal battery (no big capacity) which can be charged with multiple sources
New variants with those efficient flat solar panels on rooftop can be enabled
Charging from internal equipment grid
Charging station for low-solar sorfaces
Electric power is equally distributed between all locomotives in train and wagons can help with power too
New trains are faster with better acceleration (usig holmium magnets, low-weight components and high power), but with 50% power efficency (that power is needed to stay on tracks)
Have slighly higher capacity
Can be used on surface too (good aerodynamics and they still have wheels too)
Low health/resistances - not very good for dangerous zones
Charge state is visible as remaining fuel (sorry, no other visuals available now)
Train must be at least 10% charged to move (odd behaviour on low power)
Currently no special research - trains are unlocked by Space rails and Flat panels
And

Short variants with lower capacity can be enabled
In SE many items are needed in low/medium quantities, but many types of them are needed, so train stations for normal trains can use a lot of space
Locomotives/cargo wagons are of length 2,5 (normal size is 6), so 2 of them fits nicely in space of normal sized wagon
Short fluid wagons are of size 3 - pumps are very sensitive on positioning
Short fluid wagons must have odd number of short-sized locomotives/cargo wagons in front of them, but there can be any number of normal sized ones or short fluid wagons (see picture)

At least 1 battery must be present
Options available to enable equipment grid (on space trains only)
All locomotives/wagons with grid in train contributes to this
Settings to limit charging
- Maximum fuel state of train do drain battery (good with using solar variants)
- Minimum battery state - when that power is needed for defense
- Minimum fuel state - if it is too low, minimum baterry state is ignored (when mobility is more important then defense)

This is my first mod and i am not good at graphics (using Blender for the first time)...
I have not tested this in multiplayer
Maybe it could use some optimizations (but it seems to be not too much UPS heavy)
I am using them for some time and they works nicely

Electric fuel state visualization - but i have not needed this, so not top priority
Some optimizations
HD graphics
Graphics tweaks (like cargo wagons have no moving doors)
Better integration with some mods (for equipment grid)
Standalone variant (if needed)